In the manufacture of tires, it is conventional practice to apply one or more tire plies in cylindrical form on a tire building drum with the edges of the plies extending axially beyond the ends of the drum, then to position inextensible tire beads at the ends of the drum, and thereafter to turn up the ply edges and stitch the same around the beads and onto the outer surface of the tire ply material surrounding the drum. Although most if not all presently used first or single stage tire building machines and methods share this common practice, such machines and methods nonetheless differ in many respects.
Many tire building machines and methods presently in use employ ply turn-up mechanisms incorporating one or two expandable bladders. When brought into proper position at the end of the tire building drum and inflated, the bladder or bladders cause a previously turned down ply edge to be turned about a previously set bead at the end of the drum. As is typical of these machines and methods, the bead is set in place by an axially movable bead setting device which may also operate to contract an annular array of ply-down fingers when the latter are positioned around the ply edge. As the bead setting device moves axially toward the drum, the fingers are pivoted inwardly to turn the ply edge down over the end of the drum to provide a shoulder of ply material against which the tire bead is pressed into place. For an example of one such tire building machine and method, reference may be had to Cantarutti U.S. Pat. No. 3,438,832. As disclosed in such patent, the ply-down fingers when in an axially retracted position may provide a reaction surface operative to cause one inflated bladder to force another inflated bladder to wrap around the end of the drum.
In other tire building machines and methods, a single turn-up bladder has been employed in cooperation with a bladder pusher to effect ply edge turn-up and wrapping. Typically, the bladder pusher is in the form of a ring mounted along with a bead setting device on a carriage which actually moves to and from the drum. The carriage first moves towards the drum to set a bead carried by the bead setting device in proper position, then retracts to permit expansion of the turn-up bladder, and then again moves toward the drum to engage and push the bladder over the end of the drum. Heretofore, such bladder pushers/bead setters have been used with tire building drums which radially expand after application of ply material either to form a shoulder of ply material at the end of the drum for bead placement thereagainst or to lock in place a bead positioned by the bead setting device radially over the ply material inwardly adjacent the end of the drum. For an example of the former, reference may be had to Appleby U.S. Pat. No. 3,078,204, whereas an example of the latter can be seen in applicant's U.S. Pat. No. 4,343,671 which also shows alternative usage of a dual bladder turn-up assembly.
Notwithstanding the advances that have been made in the tire building art, some of which are noted above, there still remains room for improvement. Among existing needs are tighter wrapping of the ply material about the tire beads especially when long and hard durometer bead fillers are involved; compact wrapping with less air entrapment; less maintenance; reduction of electrical and fluid power hardware and controls; reduction of the amount of bladder expansion and pressure while providing a tight wrap; reduction of required cycle time; and uniformity of application to tires of both biased and radial ply constructions.